1. Field of the Invention
The present invention relates to optical communication equipment and, more specifically but not exclusively, to an optical feed-forward equalizer that can be used in MIMO (multiple input, multiple output) signal processing.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
The next-generation of optical communication systems is being designed for relatively high data-transmission rates, e.g., higher than about 100 Gbit/s per channel. At these rates, the effects of chromatic dispersion (CD) and polarization-mode dispersion (PMD) may significantly degrade the transmission performance of optical transport links. A representative prior-art approach to dealing with these signal impairments is to perform appropriate signal processing in the electrical digital domain, e.g., after the corresponding optical signal has been coherently detected and digitized at the receiver. This electrical digital signal processing is typically implemented using a customized ASIC, which can be relatively expensive to design and/or fabricate. In addition, such an ASIC typically requires relatively high power to operate, with the consumed power being approximately proportional to the operative baud rate squared.
The optical MIMO methods that exploit the inherently high transmission capacity of multipath (e.g., multimode and/or multi-core) optical fibers tend to further increase the complexity of digital signal processing at the receiver, e.g., because the corresponding ASIC may be additionally configured to deal with the effects of spatial-mode mixing and crosstalk in the corresponding multipath optical transport link. By some estimates, the complexity of an ASIC configured to process MIMO signals might be about one hundred times higher than that of an ASIC that does not implement MIMO processing. As a result, practical implementation and operation of an electrical digital signal processor (DSP) configured to handle the effects of CD, PMD, and spatial-mode mixing/crosstalk in an optical MIMO system might be too expensive for commercial applications.